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Electricity and Energy – Generation of Electricity: Where our electricity comes from 1
ELECTRICITY AND ENERGY
GENERATION OF ELECTRICITY:
WHERE OUR ELECTRICITY COMES FROM 1
Every day, people need electricity. Countries require vast amounts of electrical
energy for people to use – in homes, for transport and for use in industry.
For the generation of electricity, most countries use different sources of energy
to give a range of different types of input energy. This input energy is converted
into electrical energy. This helps countries to avoid having to rely on one source
of energy which may become scarce or cause pollution problems.
You can monitor the UK
electricity demand and supply
on this website: http://www.
gridwatch.templar.co.uk/
kinetic energy
electrical energy
electricity
generator
electrical
energy
condenser
water
cooler
steam
transformer
low-high
voltage
pylon
heat energy
Coal fired
The coal fired power station at Longannet in
Fife is one of the largest in Europe.
TASK
Carry out research into the different types of pollutants produced by coal fired
power stations. Write down a list of what they are, and what effect they have on
people and the Earth. Find out whether they are being replaced by other less
polluting electricity power sources.
N4_Physics_Sample.indd 14-15
water behind dam –
potential energy
Hydroelectric power stations
convert the gravitational
potential energy of water
stored behind a dam into
kinetic energy as it runs down
pipes and then into electrical
energy by generators when
the water turns turbines
connected to the generator.
water at
bottom –
kinetic energy
generator – kinetic energy
to electrical energy
The hydroelectric power station at Pitlochry
in Scotland
The power stations can only be constructed in suitable areas, such as mountainous,
or land which is at a higher level that the surrounding countryside. There is little
pollution from these power stations.
Pumped hydroelectric schemes
A pumped hydroelectric power station pumps water back up to the reservoir using
cheaper off-peak electricity at night when there is a low demand. This water flows
back down to the generator during daytime generating electricity which is sold to
customers at the peak (higher) rate.
top
reservoir
pumps/
turbines
lower
reservoir
Ben Cruachan, a hydroelectric power station
THINGS TO DO AND THINK ABOUT
Answer the following questions.
For coal fired power stations:
Scotland still relies on some coal fired power stations. A disadvantage
is pollution of gases into the atmosphere. Coal fired power stations
produce polluting gases when operating. The main pollutant is carbon
dioxide (CO2). CO2 gas is thought by many scientists to be the main
cause of global warming.
14
SAMPLE PAGES – N4 PHYSICS
THERMAL POWER STATIONS
turbine
The hydroelectric power
station uses fast moving
water to turn the generator.
ONLINE
In Scotland there are a variety of energy sources used in power stations to
supply this electricity.
In a thermal power station, a fossil fuel
chemical
(usually coal or gas) containing chemical energy steam
energy is burned to produce heat
energy. This heat energy boils water and
the steam produced turns the blades of a
turbine. The energy change here is heat
energy to kinetic energy. The rotating
turbine is connected to a generator
coal
which produces electricity. The energy
boiler
change in the generator is kinetic
energy to electrical energy.
Hydroelectric power stations
What is the energy change that takes place:
• in the boiler?
• in the electricity generator?
What is the main pollution gas produced by coal fired power stations?
What problem do many scientists think that this gas causes to our environment?
For hydroelectric power stations:
What is the energy change that takes place:
DON’T FORGET
Biomass power stations
use wood as an alternative
to coal.
• when water flows from the dam to the electricity generator below?
• in the electricity generator?
State an advantage of hydroelectric power stations compared to a coal fired power station.
Where are hydroelectric power stations most commonly found?
Give one advantage of a pumped hydroelectric station over a normal hydroelectric power station.
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Electricity and Energy – Practical electrical and electronic circuits 4
ELECTRICITY AND ENERGY
PRACTICAL ELECTRICAL AND ELECTRONIC
CIRCUITS 4
EXAMPLE 3
A series circuit containing 46 identical lamps can be
used as a decoration in houses, or on a Christmas
tree. The circuit contains lamps which operate at
5 volts, and is connected to the 230 V mains supply.
CURRENT AND VOLTAGE RELATIONSHIPS IN A SERIES CIRCUIT
Current
(a)Calculate how many lamps are required in this circuit to allow
them to operate at their suggested operating voltage.
12 volts
In a series circuit, the same
value of current is measured
at all positions in the circuit.
A4
1A
all ammeters have the same reading
I4
3Ω
I3
I2
A3
1A
A2
1A
2Ω
I1
A1
1A
total
current
from
supply
1Ω
in a series circuit, I1 = I2 = I3 = I4 …
EXAMPLE 1
State the current readings
on A2, A3 and A4 in the
following circuit.
A1
2A
A4
A3
A2
ANSWER
This is a series circuit. This means that the current has the
same value at all points in the circuit.
So A1 = A2 = A3 = A4 = 2 A
JUST A W
Voltage
Vs
In a series circuit, the supply
voltage (VS ) divides across
each component.
The voltage across each
component adds up to the
supply voltage.
EXAMPLE 2
V5
N4_Physics_Sample.indd 30-31
3Ω
8Ω
1Ω
V1
1·5
V2
4·0
V3
0·5
DON’T FORGET
In series circuits, the voltages
across each component add up
to the supply voltage.
The lamps are identical and so have the same value of resistance.
In a series circuit, if one lamp breaks, then
This means that the supply voltage will divide equally across all lamps. the circuit would be incomplete and the
other lamps would not light.
Mains voltage 230 V, voltage of one lamp = 5 V.
Number of lamps = 230
= 46 lamps required.
5
CURRENT AND VOLTAGE RELATIONSHIPS IN A PARALLEL CIRCUIT
Current
In a parallel circuit, the supply
current splits up through each
component when it reaches a
branch in the circuit. In this
circuit, the total 9 A supply
current splits up through
each branch of the circuit.
Vs
6·0V
ONLINE
total
current
IT
A6
9A
A1 + A2 + A3 = 6 + 2 + 1 = 9 A
In a parallel circuit, IT = I1 + I2 + I3 …
Voltage
total current divides
through each component
A1
1Ω
6A
A1
2A
3Ω
A1
1A
6Ω
V1
5Ω
5Ω
5Ω
V4
V3
V2
So Vresistor =
total
current
IT
To see the differences
between series and parallel
circuits in practice, watch
the video at http://www.
brightredbooks.net/subjects/
n5physics/c02_04
In a parallel circuit, the supply voltage
appears across each component
connected in parallel with the supply
voltage. The voltage across components
connected in parallel remains the same
as the supply voltage.
In a parallel circuit, VS = V1 = V2 = V3 …
The supply voltage of 6 V is measured
across each resistor connected in parallel.
V1
6V
1Ω
V2
6V
3Ω
V3
6V
6Ω
The supply voltage divides across
each resistor. Since each resistor has
the same value, the supply voltage will
divide equally between them.
5Ω
A5
9A
Vs
6·0V
ANSWER
16V
State the voltage
readings on
V2 , V3 , V4 , V5 30
est
The great
sistance
re
f
o
e
valu
e greatest
th
receives
e voltage.
share of th
supply voltage divides
across each component
V1 + V2 + V3 = 1·5 + 4·0 + 0·5 = 6 V
EE NOTE
(b)State a disadvantage of connecting the
lamps in this way.
ANSWER
SAMPLE PAGES – N4 PHYSICS
In this circuit, the value of
current measured by all four
ammeters is the same,
total
current
back to
supply
lamps
230V
Vs
4
= 16
= 4 V
4
V2 = V3 = V4 = V5 = 4 V
THINGS TO DO AND THINK ABOUT
1. A battery, resistor and lamp are connected in a series circuit.
There is a current of 2 A in the resistor.
What is the current in the lamp?
2. Three identical lamps are connected in series to a 30 V supply.
What is the voltage across each lamp?
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